The present invention relates to a guide-bar device for a multi-spindle lathe and comprises a plurality of guiding tubes, each of which supports a bar to be machined while rotating in a fluid.
Generally speaking and until now, it was not possible, with a multi-spindle lathe, to reach spindle speeds as high as the speeds now obtained with the single spindle lathes of equal capacity. However, the technological evolution of cutting tools and oils and the imperatives of the market impose a clear need to increase the speed of rotation of multi-spindle lathe spindles. In this regard, the technical evolution of the guide-bar devices for multi-spindle lathes shall, in the future, plat a prominent part, due to the fact that the mechanical devices presently in service cannot follow the potential multi-spindle lathes spindle speeds. The production capacity of multi-spindle lathes therefore depends to a large extent on improvements in guide-bar devices. The purpose of the present invention is to provide precisely such an improvement.
Known devices comprise a barrel of steel tubes, the feed of the bar being generally provided by a feed collet located at the lathe head. Due to relatively low speeds of rotation, it is relatively easy to absorb the noise created by the vibrations of the rotating bars, either by placing insulating materials around the tubes of the barrel, or by upholstering the whole aggregate in order to suppress noise from eminating toward the outside. These sound dampening means however are not satisfactory because the noise is the result of vibration and that even if one could provide perfect acoustic insulation, it would still not suppress vibrations int he bars which are transmitted along the bars to the area where the bars are machined. These vibrations degrade in the surface finish, make it difficult to hold to prescribed tolerances, and cause deterioration of the cutting tools.
From the circular of Herrmann Forch Ing., 7000 Stuttgart 80 (Vaihingen), Hauptstrase 103, Germany, a system called PLO is known which consists of modifying existing guide-bars to permit the use of machine cutting oil or emulsion for lubricating both the bar to be machined and its guiding tube, in order to produce a film of oil or emulsion for damping any vibrations induced in the rotating bar. However, such a device is not satisfactory since the rear part of the bar is not supported or centered so that the bar floats and tends to hammer the internal wall of the guiding tube when rotating. This produces noise and vibrations which are transmitted along the bar to the area where the bar is machined. Moreoever, the machine operator is obliged to use the same oil or cooling water in the guide-bar as is utilized in the machining area of the bar. However, these two environments operate under conditions which are entirely inconsistent. Fluids which are capable of producing a hydrodynamic bearing in the guide-bar application are unlikely to have the same characteristics of viscosity, emulsion, and so on as the fluid (e.g., soap water) provided for cooling the cutting tools. Moreover, the guiding tubes of the known device(s) are generally of a mechanical-welded construction. The internal diameter of the tubes of the barrel are selected in terms of the maximum capacity of the lathe. Thus it is not possible to choose the internal diameter according to changing requirements. It is also known that for realizing a hydrodynamic support it is necessary to adapt the internal diameter of the tubes to the diameter and the profiles of the bars to be machined and this in terms of the speed sof rotation that one desires to attain. Due to the fact that known devices are intended to be adapted to an existing construction, it is often difficult or even impossible to recirculate the fluid coming out from the front and rear parts of the guiding tube.
It is therefore the object of the present invention to realize a guide-bar device for multi-spindle lathe which guides, and, as the case may be, feeds the bars to be machined while eliminating vibrations in these bars in order to reduce noise. The device is capable of being adapted to all existing bar dimensions and profiles and permits easy automatization of the provisioning of new bar stock.